The present invention relates to the use of color coding to facilitate implant selection. More specifically it relates to a color coding scheme that facilitates the proper matching of three components of a modular prosthetic implant system.
Prosthetic implants have been used successfully for many years to replace degenerating or traumatized joints of the human body. Such implants typically comprise a bearing member for each side of the joint. For example, in a knee joint prosthetic implant there is a femoral component for replacing the end of the femur adjacent the knee joint and a tibial component for replacing the end of the tibia adjacent the knee joint. Likewise, in a hip joint prosthetic implant there is an acetabular component for replacing the articular surface of the pelvis and a femoral component for replacing the articular head of the femur. Implants for other joints of the body will have similar components. Each of the two components comprising an implant must attach securely to the underlying supporting tissue, usually bone, on its corresponding side of the joint. Each component must also contain an articular portion for articulating with the other component. However, within the patient population there exist variations in bone size and shape which necessitates a range of sizes of each component so as to have optimal attachment to the underlying support tissue for each patient. The differently sized components may also have differently sized articular regions. In addition, within the patient population there exist different degrees of joint disfunction which require different articular geometries for proper restoration of function.
For example, in a knee joint prosthetic implant, it is desirable for the bottom side of the tibial component to completely cover the resected tibial surface. Proper coverage results in a uniform distribution of forces, takes advantage of the strongest available bone for tibial support, and provides the largest area possible for boney ingrowth into a porous implant. On the other hand, it is important that the tibial component is not so large that it overhangs the edge of the tibia and interferes with the surrounding soft tissues. Similar constraints govern the fit of the femoral component on the resected femur. Once optimal fit of the tibial and femoral components is accomplished, the surgeon must ensure that the femoral and tibial articular surfaces will work together. If the femoral and tibial articular surfaces are not compatible, then the surgeon must alter his size choice for the tibial component or femoral component or both until a set of components that are compatible is selected. More recent knee implant systems have separated the tibial component into a base plate and an articular surface component so that there are three components between the femur and tibia which must be matched for compatibility.
Some implant systems have very limited or specific compatibility between articulating surfaces and mating components such as depicted in FIGS. 1 and 2. FIG. 1 is a cross-reference chart showing the compatibility between femoral and tibial implants. FIG. 2 is a schematic diagram showing with lines drawn between compatible components. Other systems have some flexibility in matching articulating surfaces of mating components. For example, FIG. 3 is a schematic diagram of a system in which any femoral component is compatible with any articular surface component and each articular surface component has two or more compatible tibial plates. In another example, FIGS. 4 and 5 depict an implant system in which there is flexibility in matching femoral components to articular surface components, but there is no flexibility in matching articular surface components and tibial plates.
In order to communicate the compatibility between the various components, systems have used cross-reference charts such as FIGS. 1 and 4 or color codes. The advantage of cross-reference charts is the ability to communicate compatibility of articulating surfaces and mating components for very complex systems in specific terms through the use of catalog numbers or product sizes. The disadvantage of cross-reference charts is that they are slow and cumbersome to use in an environment where speed is important. On the other hand, color coding has the advantage of being able to be used quickly and accurately. However, prior color coding systems have been able to communicate only a limited amount of information and have therefore been limited as to the complexity of the system with which they could be used.
A color coding scheme for a system like the one in FIG. 2 would be redundant with the size information since there is only one-to-one-to-one compatibility. Color coding would serve only to make the size information stand out. In a color coding scheme for this implant system typically a color code would be associated with each of the 5 sizes and each component of a particular size would be marked with the corresponding code. Prior systems have used a single color code on each system. A surgeon could quickly verify compatibility by checking that all of the components selected were the same color code. This is faster and more accurate than reading the sizes.
In a color coding scheme for a system such as the one depicted in FIG. 3, a color is associated with each group of compatible tibial trays and articular components. Each component in the group is marked with a single color code corresponding to the group color. In this system, all of the femoral components are compatible with all of the articular surface components and therefore no color code is associated with the femoral components. Verification of compatibility is accomplished if the selected tibial plate and articular surface have matching color codes.
A more complex implant system with overlapping compatibility between the femoral components and the articular surfaces is shown in FIGS. 4 and 5. Systems such as these have not previously used color coding because of their complexity and the limitations of prior color coding schemes. They have therefore relied solely on cross-reference charts such as FIG. 4.